1. Field of Invention
The present invention relates to a fluid compressor and more particularly, to a compressor for compressing refrigerant gas in a refrigeration cycle, for example.
2. Description of the Related Art
A fluid compressor disclosed in U.S. Pat No. 4,871,304 (filed on July 11, 1988 by the Applicant of the present invention), for example, is well known. The compressor of this type has a compression section driven by a motor and arranged in the closed case. The compression section is provided with a cylinder rotated together with a rotor in the motor. A piston having a center axis eccentric to the axis of the cylinder is rotatably 15. housed in the cylinder. A spiral groove is formed on the outer circumference of the piston, extending from one end to the other end of the piston in the axial direction thereof, and pitches of this spiral groove are gradually narrowed with distance from one end to the other end of the piston. A blade having appropriate elasticity is fitted into the spiral groove.
A space between the cylinder and the piston is partitioned into a plurality of operating chambers by the blade. The volumes of these operating chambers are gradually decreased with distance from the suction side to the discharge side of the cylinder. When the cylinder and the piston are rotated by the motor, synchronizing with each other, refrigerant gas in the refrigeration cycle is sucked into the operating chambers through the suction side of the cylinder. The gas thus sucked is successively fed to the operating chambers located on the discharge side of the cylinder while being compressed in these operating chambers, and then discharged into the closed case through the discharge end of the cylinder.
In the above-described compressor, however, the pressure of the refrigerant gas in the operating chamber located on the discharge side of the cylinder is higher, as compared with that of the gas in the operating chamber located on the suction side of the cylinder. Therefore, thrust force acts on the piston, heading from the discharge side to the suction side of the cylinder, to thereby increase friction between the piston and bearings. A large drive force is thus needed to rotate the cylinder and piston.
In order to solve this problem, applicants of the present invention propose another compressor in a Japanese Pat. application No 63-170693.
According to this second compressor, the piston has two spiral grooves extending from the center to both ends thereof. A blade is fitted into each of the spiral grooves. Refrigerant gas is sucked into the cylinder through the center portion of the cylinder in the axial direction thereof, fed, while being compressed in two directions or toward both ends of the cylinder, and discharged into the closed case through these ends of the cylinder.
This compressor has the following advantages. The refrigerant gas is transferred and compressed in two directions which are opposite to each other. Therefore, thrust forces which act on the piston from both ends to the center of the cylinder cancel each other out. In addition, this compressor enables stress, which acts on the blades, to be made smaller, as compared with those compressors which have a piston provided with a single spiral groove thereon and which has the same compression capacity as the above-described second compressor.
The load torque of the compressor usually changes, drawing a sine curve, as the piston rotates. Its discharge pressure also pulsates, drawing a sine curve, as the piston rotates. In the case of the compressor in which the refrigerant gas is fed, while being compressed, in two directions, both the variation in the load torque and that in the discharge pressure are about two times greater than those in the compressor in which the refrigerant gas is fed, while being compressed, only in one direction. When the load torque and discharge pressure vary largely in this manner, vibration, noise, and the like of the compressor are increased.
In order to increase the capacity of the compressor while making us of the merits available from the compressor of such type that feeds the refrigerant gas in two directions, it is therefore desired that the variation in the load torque and discharge pressure of the compressor can be reduced to a greater extent.